Embryo No. 362, .3!) mm Crown-Rump Length

Embryo No. 362 has 34 vertebrae, the first one being situated on the dorsal side of the vertebral axis, as is diagrammatically shown in figure 26. At the thirtieth and thirtyfirst vertebrie the column is bent ventrally. The eaudal end of the chorda dorsalis winds and branches in the last three vertebrae. There are 30 spinal ganglia with nerves, but the thirty-first pair of nerves has no ganglia, their degeneration probably having occurred before that of the nerves. The caudal portion of the spinal cord is divided into the conus inedullaris, filum terniinale, and coccygeal medullary vestige.

The ventriculus terminalis, which is included in the conus medullaris owing to the folding of its walls, is subdivided into two parts - an upper part, triangular in shape, and a lower, which is oblong and communicates with the upper by a narrow channel.

The filum terminale reaches from the caudal end of the conus medullaris to the ventral side of the coccygeal vestige, being enveloped by the membrane of the spinal cord, the dura mater. This embryo presents a small tail-bud at its caudal end, containing a group of cells which connects with the coccygeal medullary vestige.

↑ 8.08.1Hertig, A. T., and Rock, J. 1941. Two human ova of the pre-villous stage, having an ovulation age of about eleven and twelve days respectively. Carnegie Instn. Wash. Publ. 525, Contrib. Embryol., 29, 127-156.

↑Hertig, A. T., and Rock, J. 1944. On the development of the early human ovum, with special reference to the trophoblast of the previllous stage: a description of a normal and 5 pathologic human ova. Amer. J. Obstet Gynecol, 47, 149-184.